A series of β‐diketonate, keto(aryl)iminato, and β‐bis(aryl)iminato complexes of difluoroboron, twenty in total, have been prepared to assess the impact of chelate ring and aniline substitution on the structural, electrochemical, and photophysical properties of these ubiquitous chelates. DFT (B3LYP/6‐31G*) calculations supplemented the experimental results and both demonstrated that replacing oxygen with the more electron‐donating aniline groups serves to only fine‐tune the electronic properties because both the HOMO and LUMO energies are affected by such substitution. The electronic properties of all compounds are most greatly influenced by the nature of the substituents bound to the carbon portion of the chelate ring. Each difluoroboron complex undergoes two ligand‐based, one‐electron reductions where the first reduction potential becomes less favorable with increasing aniline substitution. Similarly, replacing oxygen with the more electron‐donating aniline groups gives rise to slightly red‐shifted absorption and emission processes. Substitution on the aniline ring has little, if any, influence on the electronic properties of the resultant complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The supramolecular structures and solution characterization of alkali metal salts of a new fourth-generation bridging scorpionate ligand, [HB(mtda)3-], containing mercaptothiadiazolyl (mtda) heterocyclic rings with both hard nitrogen donors and soft sulfur donors is reported. Key structural parameters possibly facilitating the solidstate assembly and the solution properties are described.

The second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) (mtda (Me) = 2-mercapto-5-methyl-1,3,4-thiadiazolyl) with conjoined ( N, N, N-) and ( S, S, S-) donor faces has been prepared. This second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) differs from the first-generation [HB(mtda) 3] (-) ligand by the replacement of hydrogens on the heterocyclic rings proximal to the nitrogenous face with methyl groups. This study probed whether steric interactions introduced by such methyl group substitution could modulate the reactivity and coordination preferences of these ambidentate ligands. The crystal structures of a sodium complex Na[HB(mtda (Me)) 3].3(MeOH), the potassium complexes K[HB(mtda) 3].MeOH, and K 2[HB(mtda (Me)) 3] 2.3MeOH, and several iron complexes were obtained. The difference between first- and second-generation Janus scorpionate ligands is most obvious from the discrepancy between the properties and structures of the two iron(II) compounds with the formula Fe[HB(mtda (R)) 3] 2.4DMF (R = H or Me). The complex with the first-generation ligand (R = H) is pink and diamagnetic. An X-ray structural study revealed two facially coordinated kappa (3)N-scorpionates with no bound solvent molecules. The average Fe-N bond distance of 1.97 A is indicative of the low-spin t 2g (6)e g* (0) electron configuration. In contrast, the iron(II) complex of the second-generation ligand (R = Me) is yellow and paramagnetic. This structure shows two trans-kappa (1)S-scorpionates and four equatorial-bound DMF where the average Fe-O and Fe-S distances of 2.12 and 2.51 A, respectively, are indicative of the high-spin t 2g (4)e g* (2) electron configuration. The discrepancy in binding modes and spin-states of iron(II) is carried over to the solvent-free Fe[HB(mtda (R)) 3] 2 (R = H, Me) complexes, as determined from Mossbauer spectral studies. The Mossbauer spectral parameters for Fe[HB(mtda) 3] 2 are fully consistent with low-spin iron(II) in a FeN 6 environment, whereas those for Fe[HB(mtda (Me)) 3] 2 are most consistent with high-spin iron(II) in a FeS 6 environment. Interestingly, when either complex is dissolved in highly polar solvents (DMF, DMSO, or H 2O), the ligand completely dissociates forming [Fe(solvent) 6][HB(mtda (R)) 3] 2 (R = H, Me).

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